Teclast X21, Service Manual

Page: 23 / 76

3.2.6 Charge management circuit
1. Charge management circuit mainly charges lithium-ion battery and the circuit schematic diagram
is shown in the figure 3.2.6.1:
3.2.6.1 Charge management circuit schematic diagram
2. Working principle: seen from the circuit, charge circuit is mainly fulfilled by charge control IC
ISL6294 and peripheral circuit. IN pin is power input pin of ISL6294, that is the input end of USB 5V, BAT
is output pin of ISL6294, that is the input end of lithium battery; /CHG is charge state indication end,
when /CHG is in low level, it means the charge is in process, on the contrary it means the charge is
finished; IMIN is minimum charge current setup end, that is, when charge current is less than the
current value set by this end, charge is stopped. The setup of minimum charge current is fulfilled through
selecting external resistor R20. The relationship between Minimum charge current IMIN and R20 is
shown as follows:
VCC33
P_GND
R20
510K 1%
R21
120K 1%
P_GND
Q6
SS8050LT
R22
120K 1%
P_GND
R25 10K
I_SET
C12
105/X5R
P_GND
R16
47K
R26
100K
USB_VBUS
U4 ISL6294
IN
1
PPR
2
CHG
3
EN
4
GND
5
IMIN
6
IREF
7
BAT
8
/STATUS
BAT
Seen from the above, minimum charge current is about 20 milliampere.
IREF is setup end of charge current, ISL6294 uses this reference current to charge lithium battery.
The relationship between charge current I and resistor connected externally:
REF
Triode Q6 in circuit is used for charge current selection. When users use computer to charge battery,
PNX0101 outputs I_SET, which is low level, Q6 cuts off, and R21 is connected into circuit. Seen from the
above, I is about 100 milliampere; when users use charger to charge battery, PNX0101 outputs I_SET,
EFR
which is high level, Q6 is Saturated on, R21 and R22 are connected into circuit in parallel, seen from the
- 18 -
(MA)